1. Field of the Invention
The present invention relates to a single coil and its winding former of a coil unit for a linear motor.
2. Description of the Related Art
A linear motor has a simple structure, comprises a small number of parts, and drives a moving body linearly, and its drive is precise and quick. It is widely applied to linear driving devices and positioning devices in all fields such as exposing devices for manufacturing semiconductors, and highly precise machine tools.
The linear motor generally comprises a magnetic pole unit including magnets, and a coil unit including coils, one of them is fixed to a base as a fixed body, and the other of them is connected to a moving table or the like as a moving body. The magnetic pole unit and the coil unit are placed opposing to each other at a certain gap. When a magnetic force is generated between them, the magnetic force as a thrust force drives the moving body without contact while the gap is being maintained.
A multi-pole/multi-phase DC linear motor is disclosed as one form of the linear motor. A magnetic pole unit is formed such that multiple N/S poles are placed such that neighboring poles have different polarities in this linear motor. One coil unit is formed such that multiple single coils are wired with one another as a whole.
The individual single coils constituting the coil unit have an approximately rectangular ring-like shape altogether. Two sides of the four sides of this rectangle, which oppose to each other, and are orthogonal to a moving direction, function as a pair of effective conductors contributing to generating a thrust force for a moving body of a linear motor. The other two sides opposing to each other form a pair of connecting conductors for connecting between the effective conductors, and do not contribute to generating the thrust force of the linear motor.
The thrust force F (N) of the linear motor is represented as: F=BIL where B (T) is a magnetic flux density acting on the effective conductors, I (A) is an electric current flowing thorough the effective conductors, and L (m) is the length of the effective conductors. When the number of turns of the single coil is n, F is represented as: F=BniL where i is a current per conductive wire.
Thus, it is necessary to increase the number of the turns n of the single coil for securing as large the thrust force F as possible with predetermined dimensions, or with predetermined various types of specifications of constituting members.
Because not only the area of the transverse section of the effective conductors, but also that of the connecting conductors increases as the number of turns n increases, a storage of the individual single coils becomes a problem when the multiple single coils are connected to form a coil unit.
Because the effective conductors of the individual single coils of the coil unit used for the linear motor are arranged closely to one another in a traveling direction, and the connecting conductors of the individual single coils take up spaces, it is important how to treat the connecting conductors, and then how to arrange multiple singe coils consecutively.
For example, parts close to the ends of effective conductors are bent from a coil plane (a plane including axial centers of the effective conductors) on a single coil, and three types of the single coils different in the degree of the bend are provided in the U.S. Pat. No. Re 34,674. Namely, three types of the single coils which are different in an offset of the connecting conductors from the coil plane are provided, and are sequentially arranged in a traveling direction for providing a constitution for closely arranging the effective conductors of the individual single coils while preventing interference between the connecting conductors.
However, because this constitution requires three types of single coils in consequence, the constitution has problems that the manufacturing cost increases, and the three types of connecting conductors occupy unique traveling spaces (projected areas on a section transverse to the traveling direction) respectively, thereby extremely increasing spaces around the connecting conductors as a whole.
Especially, when the number of turns of the coil n increases for increasing the transverse section of the effective conductors, thereby increasing a thrust force (a drive capability) of the motor, the transverse section of the connecting conductors increases accordingly, the space occupied by the connecting conductors becomes extremely large, and it is impossible to design a motor for increasing its space efficiency.
Also, when the entire coil unit is stored in a sealed container for cooling to avoid an effect of generated heat from the coil unit, for example, if the space occupied by the connecting conductors increases, a design for placing the magnet unit with maintaining a proper gap to the effective conductors becomes difficult while the coil unit is being stored in the sealed container.
In view of the foregoing, the inventors have proposed a single coil for a linear motor which improves these defects, and a coil unit using the same single coils in Japanese Patent Laid Open No. 2001-67955. The following section briefly describes the art because it helps understanding the problems to be solved by the present invention, and the validity of the present invention properly.
Multiple coil seats 3 shown in (a) of FIG. 8 are piled while the size is being changed gradually, a single coil 2 is formed such that ends of effective conductors 4 together with connecting conductors 6 are bent largely at an approximately right angle with respect to a coil plane CP, and the resultant single coil 2 in a saddle-like shape is used in this art as shown in (b). Single coils 2a whose connecting conductors 6 are bent toward right, and single coils 2b whose connecting conductors 6 are bent toward left with respect to a traveling direction A are alternately inserted into companion effective conductors 4a and 4b, and they are arranged closely and orderly with almost no gaps as shown in (c) of the FIG. 8. The individual single coils 2 are wired with one another according to specifications of a coil unit 10 to form the single coil unit for one linear motor.
When the single coils 2 are driven with a three-phase current, the phases of the current for the neighboring single coils 2 are shifted to one another by 120 degrees, and a three-phase coil unit with U, V, and W phases is formed. One pole, which is a constituting unit of a linear motor is defined as a part from one N/S pole to a next N/S pole in a magnet arrangement. The number of the corresponding single coils 2 (per pole) is three, and they consist of the single coils 2 for the U, V, and W phases.
Commercially available conventional coil units for linear motors including one according to the U.S. Pat. No. Re 34, 674 are formed by combining three types of single coils different in a form of connecting conductors bent toward left or right with respect to a traveling direction as a base, and has a characteristic that coil sections corresponding to three phases appear in a section perpendicular to the traveling direction (coinciding with a direction A). This means that the projected area in the transverse section in the traveling direction has an area corresponding at least three of the transverse sections of the connecting conductors.
On the other hand, the coil unit 10 relating to Japanese Patent Laid Open No. 2001-67955 includes only one type of the single coils 2, and they are simply oriented toward left or right, and combined with one another to form the coil unit 10. Thus, the coil unit 10 has a remarkable feature that the coil sections corresponding to only two phases appear in a section view of the coil unit 10. This means that projected area in the transverse section in the traveling direction basically has an area corresponding to only the two transverse sections of the connecting conductors.
In addition, the single coil 2 and the coil unit 10 according to Japanese Patent Laid Open No. 2001-67955 successfully include many strong advantages because a) only one type of single coils 2 form the coil unit 10, b) the length Wo of the connecting conductor 6 is formed as short as possible with respect to the length Lo of the effective conductor 4, and the effective conductors 4 are arranged without a gap, and c) the single coil 2 has a shape where a pair of connecting conductors 6 are bent at an approximately right angle with respect to the effective conductors 4, and the connecting conductor 6 has the shortest length, or occupies the minimum space while connecting the individual effective conductors 4.
An object of the present invention is to increase the space efficiency of the single coil including the Japanese Patent Laid Open No. 2001-67955, and is more specifically to further decrease the width of the connecting conductors protruding from the effective conductors toward left and right with respect to the traveling direction, thereby enabling a more compact structure, and simultaneously simplifying a comprehensive design including an arrangement of the magnet units.
A single coil according to a first aspect of the present invention is a single coil of a coil unit for a linear motor wherein an entire coil has an approximately rectangular ring-like shape, two sides of the rectangle opposing to each other function as a pair of effective conductors for contributing to generating a thrust force for a moving body of a linear motor, and the other two sides opposing to each other function as a pair of connecting conductors for connecting between the effective conductors. In this constitution, parts close to the ends on the effective conductors are bent at an approximately right angle with respect to a coil plane such that a pair of the connecting conductors are offset from the coil plane, and extend in parallel with the coil plane, and the transverse section of the connecting conductors is in an approximately trapezoidal shape including parallel sides approximately perpendicular to the coil plane, and a tilted side opposing to the coil plane, and tilted in a direction opposite to the direction of the offset of the connecting conductors in this extending state where the coil plane is defined as a plane including individual axial centers of a pair of the effective conductors.
In this single coil, the parts close to the ends of the effective conductors are bent at an approximately right angle with respect to the coil plane, and bending at an approximately right angle offsets (separates in parallel) the connecting conductors from the coil plane. Then, the transverse section of the connecting conductors is in an approximately trapezoidal shape, and especially parts opposing to (facing) the coil plane is in a form xe2x80x9ctiltedxe2x80x9d toward the direction opposite to the direction of the offset of the connecting conductors.
As a result, the offset length of the connecting conductors decreases further, thereby further decreasing a projected area of the connecting conductor on a transverse section in a traveling direction when the single coils are used to from a coil unit. The effects brought about by this xe2x80x9ctiltingxe2x80x9d will be described later in detail.
An outer periphery of the connecting conductor is perpendicular to or parallel with the coil plane because the transverse section is in a trapezoidal shape, thereby providing a proper fit to an mounting member or a magnetic pole unit.
A coil unit according to a second aspect of the present invention has a feature that the tilted angle of the tilted sides with respect to the coil plane is set in a range from 3 to 30 degrees.
The second aspect of the invention more specifically embodies the first aspect of the present invention in terms of xe2x80x9cthe angle of the tiltxe2x80x9d. According to the first aspect of the invention, a more or less effect can be provided when the connecting conductors are offset while the connecting conductors are bent at an approximately right angle, and simultaneously xe2x80x9cthe tiltxe2x80x9d exist. However, when the tilt angle is set in the range from 3 to 30 degrees according to the second aspect of the invention, its effect can be obtained more clearly. A more preferable tilt angle exists in a range from 5 to 20 degrees.
A coil unit according to a third aspect of the present invention has a feature that the effective conductors have side surfaces parallel to the coil plane, and the tilted sides are positioned between a plane including the side surfaces on a side toward which the connecting conductors are offset, and the coil plane.
The third aspect of the invention further embodies the first aspect of the present invention in terms of xe2x80x9cthe position where the tilted sides are formedxe2x80x9d. Forming the tilted sides at this position can place the connecting conductors so close to the coil planes as a part of the transverse sections of the connecting conductors surely overlap an extension line from a transverse section of the effective conductors, thereby decreasing the offset length down to approximately the minimum.